Look at the rear disc. What would cause this? I have the same issue on both inner sides of the rear discs. The outside of both rear discs is fine. I have stock PBR's.

Calipers? I'd like to know for sure since auto stores rape us on rear calipers.

 

I'd take a better pic but the car's at the shop getting sub-frames welded in.

What's happening is i'm only getting brake pressure at the innermost section of the rotor. There's about 1/2 inch of rust at both the outer and inner areas of the inside of the rotor. So apparently i'm only using the middle 1/2 inch or so of the rotors to stop.

Would bad calipers cause this or is it something else?

 

Car's back and rotor's off.
Could this be caused by:

bad caliper
bad MC
bad prop valve

Something else?

 

Everytime I've had that problem, on any car, new rotors and pads have fixed it.

I don't know what causes it, but that's my solution.

 

Firebird actually had a recall on the rear calipers back in the 80's due to not functioning right i had to take mine in and they replaces the calipers.I was having the same problem.changing brakes and rotors will temperarely fix the problem.
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Firebird actually had a recall on the back brake calipers due to not functioning right.I had to take mine in and the dealership replaced both back calipers.

 

Wrong. He has PBR calipers, not the iron Delcos.

The rotors are old and used up. Look at them, the iron is flaking off in chunks.

New rotors alone would probably fix the problem, but it's a dumb move to put old pads on new rotors, IMO. With factory build tolerances and the way these things wear (pad taper, etc), you're asking for problems.

 

I have new pads and rotors but I don't want to put them on if i'm having caliper issues.
I've never had to mess with my rears on this car before but I don't believe I was able to compress the caliper piston as far in as it should go. My experiences with other calipers is telling me something's not right.

Nape, you're correct. You must've noticed it in the picture. I shoulda mentioned it before. I have PBR rears.

 

I would go for the prop valve. What are the chnaces that both of the rear calipers are bad (slim to none). Sine the front brakes have no issues it must not be the master cyliner.

 

I still need to take the other side off. The front's had their own issues but at least it was using all of both sides of each rotor.

If it matters, my e-brake is virtually useless.

 

Just took the other side off. That piston compressed fully. So looks like I have 1 bad caliper and still a different problem. I say different problem because both rear rotors are doing the same thing with apparently only 1 bad caliper.
Maybe it is the prop valve. Yay? Nay?

 

What are you using to compress the piston? You took the cap off the master cylinder, right?

Not sure how long you've owned the car, but if you've never touched the rear brakes, a previous owner could've only changed a rotor on one side while just turning the other. I'm not trying to BS ya, a pad and rotor swap will fix that.

I ran into this problem when I bought my van and when I did the brakes on my dad's S10 this summer and it was on the front brakes. Both vehicles went from stopping poorly even with high pedal effort to stopping well afterwards and there hasn't been a caliper issue on either vehicle.

I'm not sure if it's a rotor quality issue, but in my experience it seems that once the rotors get old enough they just start to scale/flake off.

 

Before you buy anything else check the pressure before the prop valve and after the prop valve. Be careful not to get air in the system. If there is a difference in pressure it is your prop valve that is bad.

 

I used a big c-clamp to compress the piston. The cap is off the MC. In fact, there's no fluid in it. Removing the K-member forced me to remove the front brake lines. Figured might as well empty the master cylinder and flush the whole system while I was at it. That and I upgraded to the LS1 fronts at the same time. Nothing has been run yet as this rebuild is basically 80% of the car.

I'm sure there's air in the system at this point. For now i'll just replace the one caliper, both rotors, rear pads, flush the system, and check the pressure once I can get the car running. How do I check the pressure?

 

Wear like that doesn't necessarily mean a caliper problem. When I worked at GM dealerships the mid to late 90's W and N bodies had major problems with brake rotors warping and flaking like yours some with only 15-20K. Gm tried to use a composite material in the rotors and some had very low quality metal for cost and weight savings. Since you have a portion of the rotor that does show normal wear I would think caliper problems are lowest on the list of causes. From my experience it is inferior metal used to make the rotors. I have seen best results with Raybestos or Wagner rotors, and biggest problems with Aimco or other cheaper parts. Replace them and the pads with good quality parts and I would almost wager your problem will not return.